A device identifying method for identifying whether a candidate member device belongs to a device set or not by an identifying device. The device set comprising at least one member device. The method comprises: (a) establishing a connection between the identifying device and a first member device among the member device, to acquire a set ID and at least one identifying key from the first member device; (b) discovering the candidate member device according to the set ID; (c) generating identifying data according to the identifying key and transmitting the identifying data to the candidate member device; and (d) determining whether the candidate member device belongs to the device set or not according to a comparing result for the identifying data.